This invention relates to the manufacture of fatty acid amides from fatty acids and amines, particularly alkyl polyamines. In particular, it relates to such methods which yield fatty acid amides with relatively low color.
Fatty amides made from a fatty acid and an amine (particularly an alkyl polyamine) have utility as fabric softeners. Fatty materials in general, fatty amides being no exception, are prone to developing undesirable color upon chemical reaction, heating, and storage. However, consumer uses for fatty amides such as fabric softeners require low color, and high color fatty amides are not saleable in such applications.
One approach to decoloring fatty materials in general is to recrystallize the product. This however, causes product loss and is otherwise expensive. Another approach is to distill the colored product. This is again expensive, and can result in additional color formation if heat is used in the distillation. Yet another approach is the use of liquefied hydrocarbon gases such as propane to extract colored components. This last approach, however, is both expensive and poses an additional safety hazard because of the flammable or explosive nature of such gases. One problem unaddressed by these solutions is that after decolorization, the fatty materials will tend to become colored during storage.
U.S. Pat. No. 2,828,320 (Gibson-Swift & Co., 1958) teaches stabilization of the color of previously decolorized fatty acids with a blend of hypophosphorous acid and one of di-tertiarybutyl para cresol (BHT), butylated hydroxy anisol, beta napthol, propyl gallate, or hydroquinone. This patent does not, however, address the problem of color formation during reaction and does not address the possible reaction of the stabilizer materials with the intended reactants.
Japanese publication 35528/1970 (Fuchizawa-Japan Ushi (Oil and Fat) Co., 1970) specifically addresses the production of fatty acid bisamides, and uses a mixture of (1) a phosphorous acid, a hypophosphorous acid, or an alkali or alkyline earth salt thereof, and (2) an alkali borohydride. This process, however, does not stabilize the color of the product as much as would be desired.